New Electric Brakes not working

[64Overlander]

I recently had new electric brakes put on my 64 Overlander and had all the running lights checked, new plug put on and new brake controller installed on the truck. The brakes worked great for 1-2 weeks then quit working. I still have running lights on the trailer and had the brake controller checked in the truck which was functioning properly. The shop indicated that a "loose" ground wire was probably the culprit in the trailer. Would anyone happen to know where this might occur?

Thanks.